support returning raw_response for anthropic for enabling thinking mode as a beta feature

[narengogi]

Related Issues:

• [Feature] Return provider raw/untransformed response when 1:1 mapping with openai fields is not possible #964

To receive raw_response along with the transformed response, please include the following header when making your requests: x-portkey-include-raw-response: true

Testing Done

• non-streaming anthropic calls with x-portkey-include-raw-response set to false and true
• streaming anthropic calls with x-portkey-include-raw-response set to false and true
• Test one other provider with streaming and non-streaming to make sure the streamHandler changes are working correctly

Note
this PR adds support for raw_response in non-streaming responses only